1. Field of the Invention
The present invention relates to manufacturing of integrated circuits on semiconductor substrates and, in particular, to etching of organic films on such semiconductor substrates.
2. Description of Related Art
In lithographic processing of semiconductor wafer substrates, a photoresist layer is deposited and patterned by selective exposure to an energy beam, developing and etching to form patterned exposed area, which are then used to selectively etch underlying layers. The extension of 248 nm lithography has in many cases led to the introduction of more sensitive photoresists. Many of these photoresists have demonstrated poor performance with traditional etch processes. Deep ultraviolet (DUV) photoresists have demonstrated increased sensitivity to etch processes for the underlying layers. This has been an important issue with regard to etching of underlying organic coatings, particularly organic anti-reflective coatings (ARC), which are in turn applied over dielectric layers. Opening to an organic ARC (anti-reflective coating) layer is often the most challenging step in which to maintain photoresist integrity.
High density plasma (HDP) etching tools, when applied to organic ARC etching, have suffered from poor DUV photoresist protection due to their aggressiveness, e.g., high ion flux and high dissociation fraction. This has made implementation of the HDP sources for dielectric etching difficult.
The photoresist damage is typically addressed by the application of a less aggressive etch process, i.e. lower power and less reactant flow. As a result, very mild etching conditions have typically been necessary for etching the organic layer to avoid damage to the overlying photoresist layer. Organic ARC is, from an etch perspective, similar to photoresist, and the ARC etch will typically strongly impact the photoresist as well. For this reason, the ARC open for sensitive photoresists has been performed in a traditional low power plasma etch tool to minimize damage, presumably by limiting the etch rate and reactant flow. However, much of the throughput advantage of a high density plasma tool is lost when a conventional tool must be used to open the ARC layer, as it in turn leads to a loss of etch rate and possibly a reduction of anisotropy.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an improved method of etching of organic layers, especially organic ARCs, selective to patterned photoresist layers.
It is another object of the present invention to provide a method of etching organic layers on a semiconductor wafer substrate which has higher etch rates without damage to the photoresist layer.
A further object of the invention is to provide a method of increasing organic layer etch throughput using available etching equipment.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a method of etching an organic film layer underlying a patterned resist layer on a semiconductor substrate. The method comprises providing a substrate having an organic film layer and a patterned resist layer overlying the organic film layer. The patterned resist layer has spaces exposing areas of the organic film layer. The organic film layer and the resist layer being of differing composition from each other. The method includes contacting the exposed organic film with an etchant comprising a fluorocarbon and nitrogen in the presence of a plasma-generated energy and removing exposed areas of the organic film with the etchant.
Preferably, the plasma is a high density plasma and, during the plasma etching, there is applied a plasma source power of about 300 to 2500 watts and a bias power applied to the wafer of about 100 to 1000 watts, at an operating pressure of about 2 to 20 mTorr. The etchant preferably comprises about 50 to 95 volume percent argon, about 5 to 40 volume percent C4F8, and about 5 to 60 volume percent nitrogen. More preferably, the fluorocarbon is C4F8, and the etchant further includes a noble gas, for example, argon.
The method is particularly useful where the organic film is an organic antireflective coating, and the resist layer comprises a deep ultraviolet resist material. The patterned resist layer is consumed more slowly than the organic film layer, and the etchant removes substantially all of the organic film in the area contacted by the etchant. The substrate may include an oxide layer underlying the organic film layer, such that the etchant removes substantially all of the organic film in the area contacted by the etchant and exposes an area of the oxide layer, and the oxide layer is substantially undamaged after contact with the etchant.